Logging wells during drilling



Nova 18, 1941. R. w. STUART 2,253,198

LOGGING WELLS DURING DRILLING Filed July 16, 1940 2051mm #1 [liar Z Patented Nov. 18, 1941 LOGGING WELLS DURING DRILLING Robert W. Stuart, Tulsa, Okla., asslgnor to Stanolind Oil and Gas Company, Tulsa, Okla., a corporation of Delaware Application July 16, 1940, Serial No. 345,867

7 Claims.

This invention relates to the logging of wells during the drilling thereof and more particularly to the logging of wells being drilled by the rotary method employing a continuous stream of a drilling fluid. Still more specifically it relates to a method and apparatus for detecting the presence and amount of crude oil present in formations being penetrated by the drill bit.

With the increasing realization of the importance of a thorough knowledge of the nature and fluid content of subsurface formations and their exact depth, various instruments and methods have been devised to assist in obtaining this information. The instruments now in use include coring equipment, electrical logging units, side wall samplers, and drill stem fluid testers.

In order to eliminate the possibility of drilling through oilor gas-bearing formations, it is customary to take cores of any formations likely to contain these constituents, and to subject these cores to various laboratory tests. This is a slow and expensive procedure which usually does not give as much information as desired. Furthermore the inevitable delay connected with this procedure either causes the drilling operation to be held up until the test results are available or necessitates further drilling without the benefit of these results and with the consequent danger of drilling through productive formations.

Another widely applied method is electrical logging which is based upon differences in the electrical characteristics of different formations. Normal electrical logging can be carried out only after the well has been drilled and does not give the desired information when it is most useful, which is at the time the particular formation is being penetrated. Also, in many cases such logs Other methods such as side 'wall.

mation penetrated by the drill bit is drilled up and carried by the circulating drilling mud'to the top of the well. If the formation penetrated contains a fluid such as oil, gas or salt water, therefore, the presence of these-substances can be determined by appropriate tests applied to the drilling mud returns. Since the hydrostatic mud the hole from the bottom and by continuously pressure is greater than the pressure existing in any formation, the only formational fluids present in the drilling mud will be those contained in that part of the formation which has been drilled up. Accordingly, by correlating the results of various tests performed on the returning mud with the depth at which the particular portion thereof being tested picked up portions of the formation, a complete log of the nature, extent and depth of the various formations traversed by the well can be obtained, and is made available during the drilling operation.

There are a number of different tests which can be applied to drilling mud returns advantageousl and preferably a number of them are used simultaneously so that the most complete picture of the nature of the strata being penetrated is obtained. Among these tests are tests for crude oil, hydrocarbon gas, electrical conductivity and hydrogen ion concentration. The present invention, however, is concerned principally with that aspect of mud logging technique which has to do with the determination of the presence and amount of crude oil in formations being drilled, and comprises a simple and advantageous method and apparatus for continuously determining the content of crude oil in drilling mud as it returns to the surface of the earth.

It is therefore an object of my invention to provide a method of continuously determining the presence and amount of crude oil in a stream of drilling mud and apparatus for carrying out this method. Another object is to provide a novel method of mud logging. A further object is to provide a novel crude oil detecting unit adapted to measure and record most efficiently the amount of crude oil present in a flowing stream of drilling fluid or the like.

Further objects, uses and advantages of my invention will be apparent from the following detailed description read in conjunction with the drawing, in which:

Figure 1 illustrates schematically one form of apparatus according to my invention; and

Figure 2 shows in vertical cross-section a preferred form of oil-detecting unit according to my invention together with a conventionalized diagram of the electrical circuit associated therewith.

In one of its broadest aspects my invention comprises the determination of crude oil in formations encountered during a rotary drilling operation by'causing the drilling fluid to pass up testing the flowing stream for crude oil at the top of the well. This test is made by subjecting the stream of drilling fluid-to irradiation by It is recognized that crude oil has heretofore been detected in drilling mud returns by perlodically subjecting samples thereof to irradiationwith ultraviolet light and observing whether or not fluorescence is produced. This is obviously haphazard and tedious and each sample must be placed in a clean vessel for observation, since minute amounts of crude oil remaining from one test to another would cause erroneous indications. One of the features of my invention is that my oil-detecting unit is so designed that the crude oil passes through it completely, thus making continuous testing of drilling fluid for crude oil possible.

Furthermore continuous testing and recording has another important advantage due to the fact that crude oil as'well as gas and salt water is a fluid which slowly migrates in relatively small amounts from formations containing it to the strata immediately overlying them. Penetration of these strata will result in the immediate detection of minute amounts of crude oil by my invention and indicate that the drill bit is probably approaching a formation productive of crude oil. Appropriate measures can then be taken.

My invention can best be understood in all its details by reference to the drawing together with the following description. Figure 1 shows in highly diagrammatic form a well bottomed at l I which has penetrated two different formations I 2 and I3. For purposes of this description it will be assumed that formation I3 contains crude oil, although it will be understood that it may contain gas or salt water or may be a shale, limestone, etc., containing no fluid. As shown well ID has a casing l4 within the upper portion thereof supported by landing base l5, which also supports means for controlling and withdrawing drilling mud from the well, represented by master valve l6, blowout preventer l1 having a mud outlet l8 and fill up line connection I9, and nipple 20.

Well I8 is being drilled in the usual manner by means of rotary table 2|, kelly 22, drill pipe 23 and bit 24 and is equipped with the conventional derrick 25, derrick floor 26 and derrick supports 21. Drilling mud-is withdrawn from mud pit 28 through line 28 and forced by means of pump 30 through line 3|, hose 32, swivel 33, kelly 22, drill pipe 23 and the usual openings in bit 24 to the bottom ll of well I0, where it picks up cuttings of the formation being drilled. Then the mud passes up the annular space around pipe 23 and the bulk thereof flows out mud outlet I8 and line 34 to pit 28, thus completing the cycle. A great many details have been omitted from the drawing in order to simplify it, but these can readily be supplied by those skilled in the art. For example, the mud returning through line 34 would normally be screened to remove cuttings, and means are of course essential to support, raise and lower the drill string and to rotate table 2|. These and other items, however, are not necessary to an understanding of my invention.

A portion of the returning mud containing portions of the formation being penetrated by bit 24 passes through fill up line connection [9 and line 35 to a crude oil testing unit capable of continuously measuring and preferably recording. the

amount of crude oil present therein. As mentioned above a number of other test's are also preferably applied to the mud stream at the same time and. units capable 'of carrying out. these tests are therefore diagrammatically represented.

as tobe portable, for instance in a truck or trailer,

, and are arranged to give continuous or substantially continuous records'on aichartor charts, which can be arranged to move at a'rate proportional to time or depth, but p referably'are driven by suitable apparatus at a rate such that the records are plotted directly against the depth at which the portion of the mud under test was at the bottom of the well'and picked up the drilled up formational material contained therein.

In carrying out my invention drilling proceeds in the usual manner by rotation of table 2! and mud is continuously circulated by means of pump 30. If it is assumed that well 10 has not yet penetrated formation I3 but is approaching it, unit 3! will gradually show a slowly increasing amount of crude oil and, if gas is associated with the oil in formation l3, unit 36 will also show an increasing concentration of gas in the mud returns. In this way the proximity of formation l3 can be predicted, and the actual penetration thereof will be clearly indicated by rather sudden increases in the gas and crude oil readings. In the meantime units 38 and 38 may show deflections of the recorders associated therewith depending upon the nature of formation l2.

As pointed out above, the present invention relates primarily to the detection and measurement of crude oil in subsurface formations penetrated during the drilling of a well by the rotary method, and is based upon the known principle of subjecting samples of returned drilling fluid to irradiation with ultraviolet light and using the resultant fluorescence as a measure of the presence or absence of crude oil. This fluorescence appears to be a property of the rather complex composition of the crude oil since fluorescence of a different wave length is produced when refined oils, such as lubricating oils, are irradiated in this manner. A preferential indication of the presence and amount of crude oil is obtained by the use of suitable optical filters which allow only the fluorescent light emitted by irradiation of crude oil to pass them. A preferred form of crude oil detecting unit according to my invention is shown in Figure 2 and will hereinafter be fully described.

Gas analysis unit 36 is not shown in detail since it consists essentially'of apparatus for removing gas from the stream of mud under vacuum, mixing it with a stream of air, passing the mixture over a resistance wire maintained at a definite temperature by means of an electrical current and measuring the rise in temperature by means of a circuit adapted to measure the corresponding increase in the value of the resistance. This apparatus is simple and can easily be constructed byone skilled in the art.

The electrical conductivity test can be carried out by means of unit 38 in a manner well known to those skilled in the art, and is indicative of the presence of salt in the drilling mud and hence of salt or salt water in the formation being drilled because the presence of salt very materially increases the electrical conductivity of drilling muds. The pH unit I! can also be constructed to operate according to known principles and serves to indicate the presence of substances such as anhydrite, gypsum or limestone in subsurface formations as well as to aid in determining whether or not the mud needs treatment prior to recirculation.

In addition to the above, other tests may be continuously applied to the mud stream flowing through line 35. For example knowledge of the density and viscosity of the returning mud is very helpful. Also other types of data may be recorded which aid in giving a more complete picture of the progress of the drilling operation and of subsurface conditions, and examples of such data are drilling rate, mud pump rate, torque applied to the rotary table, weight'suppor'ted by the cable, etc.

One feature has been described which is very important particularly when the presence and amount of gas in the drilling mud returns are determined, and that is the mode of sampling.

It will be understood that my invention can be carried out by closing fill up line connection I! and connecting line 35 with line 84, but if this were done there would be considerable danger of loss or separation of gas and of pollution of the returning mud with oil from the derrick floor, so that a stream of mud obtained in this way would not be representative and might give totally erroneous results. By continuously bleeding off a sample of the thoroughly agitated returning mud from the fill up line connection immediately below the blowout preventer as shown in Figure 1 or at a point similarly located below the principal mud outlet, a continuous representative sample is obtained which will permit quantitative testing of the mud and consequently a more accurate evaluation of the formation characteristics.

From the above it will be apparent that I have described in its broad aspects a novel and emcient method of determining the presence and amount of crude oil in subsurface strata penetrated by the drill bit during a rotary drilling operation and one which can be applied to a well being drilled simultaneously with other test methods adapted to round out a complete picture of formational conditions. This method has been described in connection with an ordinary drilling operation, but it can be applied also to reverse circulation drilling, i. e., drilling with the mud forced down the annular space surrounding the drill pipe, and up the interior thereof.

The method of logging wells described herein is the only reliable one when pressure drilling is employed. This typeof drilling which consists essentially in applying back pressure to the drilling fluid leaving the hole, has become very important in the drilling of deep high pressure wells. Generally a check valve is placed in the drill collar so that the pressure on the drilling fluid within the well will not be relieved when making up extra sections of drill pipe. This check valve makes it impossible to core drill in such wells, and all electrical logging methods known at present can not be utilized because of the impossibility of introducing the cable into the high pressure well bore. Finally, even the cuttings in the returning drilling fiuid yield little information because they are very considerably device used to maintain back pressure. Obviously these considerations do not affect the results obtained by mud logging, but demonstrate the particular value of the present invention for pressure drilling work.

Referring now to Figure 2 showing a preferred form of crude oil detecting and measuring unit. drilling mud returning from the well flows through a closed channel 50 from inlet II to outlet 52, thus presenting a continuously changing surface 51 to the irradiating and detecting portions of the unit by virtue of opening 54 in the upper portion 55 of channel 50. Mounted on portion 55 of channel I0 and completely surrounding opening 54 therein is a short riser 56, and the resultant upwardly facing opening is completely covered by a window 51 made of quartz or other transparent material capable of transmitting ultraviolet as well as visible lightl- Immediately above window 51 is a light-proof by case 58, and'as' shown extends therethrough at an angle which will be discussed below.'

Chamber 5! contains a source of ultraviolet light 60 actuated by electrical current supplied through conductors 6| from a suitable battery or generator. The source of ultraviolet light 60 is preferably a lamp of the conventional mercury vapor type. Chamber 59 has at its lower end an opening 62 for the emission of ultraviolet light across which filters 63 and 64 are mounted, these filters being capable of substantially completely removing both visible and infra-red rays. The entire arrangement is such that ultravioletlight from lamp it passes through filters 63 and 84 and window 'S'I'and irradiates the surface 53 of the mud flowing in'channel ill. ,,A lso mounted within casing 58 by means of bracket is a photo-sensitive cell 66 enclosed in a light Proof chamber 81 having a downwardly facing opening--68 for the admission of light, which opening, however, is covered by a filter 69 adapted to transmit visible light and remove ultraviolet rays.

Photosensitive cell 68 and filter 69 are arranged in such a way as to receive with a maximum of efficiency any fluorescent light produced by crude oil in the mud flowing below window 5] under the influence of the ultraviolet light di rected against it from lamp 60. I have found that the maximum fluorescent emission is obtained when the angle between the axis of emission of ultraviolet light through filters 83 and 84 and the surface 53 of the mud is of the order of 45, but this angle may vary between about 40 and about 50 with goodresults. Furthermore maximum energization of photosensitive cell 66 with minimum transmission of ultraviolet radiation to this cell is obtained when the included angle between the fluorescent rays reaching it and the axis of ultraviolet light mentioned above is about 20 to 40, preferably about 30.

Photosensitive cell 66 can be of any suitable type. For instance it can be of the photovoltaic type such as a copper oxide. silver or selenium cell which requires no auxiliary source of potential, and gives voltage variations responsive to the amount of light received which can be recorded directly or after amplification. In the preferred apparatus of Figure 2, however, photosensitive cell 66 is of the photoconductive type, for instance a gas-filled tube using a metallic rubidium electrode. The power to operate this cell is provided by battery 10 and leads II, one of which has a resistance 12 in the circuit. The

variations of conductivity of cell 86 responsive to the fluorescent light received are measured by determining the potential difference across resistance 12, which potential difference can be supplied directly to a suitable recorder.

Preferably, however, some amplification 13 used, and two stages of resistance-coupled amplification are schematically shown. Detailed description of this is believed to be unnecessary, since it will be apparent that the potential difference across resistance 12 is applied by means of conductors l3 and 14 to the grid of vacuum tube 16, which has a. plate circuit including battery I1 and resistance 18. Suitable grid bias for this tube is supplied by battery 11 and voltage divider 15. Increase in the conductivity of cell 66 will therefore cause an increased negative potential difference across resistance 12 which when impressed upon the grid of tube 16, causes greatly decreased current flow in the plate circuit thereof and a correspondingly decreased potential difference across resistance 13. This last-mentioned potential difference is applied to the grid of tube 19 by means of conductor 80 and a filament connection 8| leading to voltage divider 82 shunted across battery Tl, this grid voltage being kept at a proper value when no light reaches cell 66 by proper adjustment of voltage divider 82. Changes in potential difference across resistance 18, however, are applied in full to the grid of tube 19, which again results in a greatly amplified plate current and a change in potential difference across resistance 83, which is impressed by leads 84 upon a recorder 85 having a pen arm 86 cooperating with a moving recording medium 87 to provide the desired record.

A very important feature of my novel crude oil detecting unit is the provision of means for preventing window 51 from becoming contaminated. I have found that crude oil has a marked tendency to cling to window 51 if it comes in contact therewith .and that even if no contact is permitted, window 57 easily becomes spattered with mud and rendered substantially opaque unless special precautions are taken. One procedure which has been found reasonably effective is to provide water jets for washing the surface of window 51 and wiping means of the windshieldwiper type which together will continuously coperate to keep window clean and free from contamination. However, my preferred means for accomplishing this result is shown in Figure 2, and consists in its simplest form essentially of keeping the surface 53 of the mud stream at a distance from window 51 by means of riser'56, thus creating an air space 88 above the mud, and supplying air slowly to air space 88 through line 89. In this way any tendency that the mud may have to rise into space 88, or to spatter or to increase the humidity in space 88 to the dew point is substantially eliminated. I have also provided a plurality of water jets 90 supplied by annular conduit 9| through line 92 and valve 93, which can be used periodically to wash the lower surface of window 5'1 if for some reason that should be desirable.

Many modifications of my invention will be apparent from the above. For example, window 51 can be eliminated if casing 58 is made reasonably gas-tight as long as chambers 59 and 61 are far enough away from surface 53 of the mud.

In another modification a photosensitive medium such as a photographic film can be used in place of a photosensitive cell and the devel oped film run through a photoelectric scanning system. In this case it is desirable to expose only one-half of the film and use a double scanning system to eliminate developing differences in background. Another possibility is to mask alternately the source of ultraviolet light and one or more photoelectric tubes. Since there is a time lag between irradiation and the beginning of fluorescence, by choosing the proper masking frequency a series of electrical variations can be obtained which can be amplified very efllciently.

While I have described my invention in terms of certain specific embodiments thereof, I do not desire to be limited thereto, but only by the scope of the appended claims.

I claim:

1. Apparatus for detecting crude oil in a flowing fluid stream comprising a conduit for said stream having an upwardly facing opening therein, a light-proof case mounted on said conduit and completely covering said opening, said case comprising an air-tight chamber above the surface of said stream, means within said case for directing ultraviolet light against the surface of said stream through said opening, means within said case responsive to the intensity of fluorescent light produced by the action of said ultraviolet light on crude oil in said stream, and means for introducing a stream of air into said chamber.

2. Apparatus for detecting crude oil in a flowing fluid stream comprising a conduit forsaid stream having an upwardly facing opening therein, a light-proof case mounted on said conduit and completely covering said opening, means within said case for directing ultraviolet light against the surface of said stream through said opening, means within said case responsive to the intensity of fluorescent light produced by the action of said ultraviolet light on crude oil in said stream, a window adapted to transmit both visible and ultraviolet light mounted within said case between said opening and said lightdirecting and light-responsive means, whereby an air-tight chamber is formed below said window and above the surface of said stream, and means for introducing a stream of air into said air-tight chamber.

3. Apparatus for detecting crude oil in a flowing fluid stream comprising a conduit for said stream having an upwardly facing opening therein, a light-proof case mounted on said conduit and completely covering said opening, a source of ultraviolet light mounted within said case, means for directing said ultraviolet light against the surface of said stream at an angle in the range from about 40 to about 50, a window adapted to transmit both visible and ultraviolet light mounted within said case between said opening and said directing means, whereby an air-tight chamber is formed below said window and above the surface of said stream, means for introducing a stream of air into said chamber, a photoelectric cell mounted within said case so as to receive most efliciently through said window fluorescent light produced by the action of said ultraviolet light on crude oil in said stream radiated from said surface at an angle about 20 to about 40 greater than said firstmentioned angle, and means for recording electrical variations generated bysaid photoelectric cell.

4. The method of detecting crude oil in subsurface formations encountered in a well during a rotary drilling operation employing a circulating stream of drilling fluid which comprises flowing at least a portion of said drilling fluid returning from the bottom of said well in a continuous stream so as to present a quiet continuously changing surface, directing ultraviolet light against said surface at an angle of about 40 to about 60 whereby visible light is produced by fluorescence of crude oil present in said fluid, receiving visible light radiated from said surface at an angle of about 20 to about 40 greater than the aforementioned angle, transforming said received light variations into electrical variations, and recording said electrical variations.

5. Apparatus for detecting crude oil in subsurface formations encountered in a well during a rotary drilling operation employing a circulating stream of drilling fluid comprising means for flowing at least a portion of said drilling fluid returning from the bottom of said well in a continuous stream, means for directing ultraviolet light against a continuously changing surface presented by said stream at an angle of about 40 to about 60, and means responsive to the intensity of visible fluorescent light radiated from said surface at an angle about 20 to about 40 greater than said first-mentioned angle.

6. Apparatus according to claim 5 wherein said light-responsive means includes a photoelectric cell of the photoconductive type, and wherein means are included for recording electrical variations produced by said cell.

'7. Apparatus for detecting crude oil in a flowing fluid stream comprising a conduit for said stream having an upwardly facing opening therein, light-proof means completely covering said opening, a source of ultraviolet light within said light-proof means, means for directing ultraviolet light from said source through said opening against said stream at an angle of about 40 to about 60", a photosensitive cell within said light-proof means mounted to produce electrical variations responsive to variations in the visible fluorescent light radiated from said stream at an angle about 20 to about 40 greater than said first-mentioned angle, and means for recording said electrical variations.

ROBERT W. STUART. 

